1. Field of the Invention
The present invention relates generally to memory, and more specifically to memory employing a cross point array.
2. Description of the Related Art
Conventional nonvolatile memory requires three terminal MOSFET-based devices. The layout of such devices are not ideal, usually requiring feature sizes of 8f2 for each memory cell, where f is the minimum feature size.
However, not all memory elements require three terminals. Certain complex metal oxides (CMOs), for example, can retain a resistive state after being exposed to an electronic pulse, which can be generated from two terminals. U.S. Pat. No. 6,204,139, issued Mar. 20, 2001 to Liu et al., incorporated herein by reference for all purposes, describes some perovskite materials that exhibit such characteristics. The perovskite materials are also described by the same researchers in xe2x80x9cElectric-pulse-induced reversible resistance change effect in magnetoresistive films,xe2x80x9d Applied Physics Letters, Vol. 76, No. 19, 8 May 2000, and xe2x80x9cA New Concept for Non-Volatile Memory: The Electric-Pulse Induced Resistive Change Effect in Colossal Magnetoresistive Thin Films,xe2x80x9d in materials for the 2001 Non-Volatile Memory Technology Symposium, all of which are hereby incorporated by reference for all purposes.
Similarly, the IBM Zurich Research Center has also published three technical papers that also discuss the use of metal oxide material for memory applications: xe2x80x9cReproducible switching effect in thin oxide films for memory applications,xe2x80x9d Applied Physics Letters, Vol. 77, No. 1, 3 Jul. 2000, xe2x80x9cCurrent-driven insulator-conductor transition and nonvolatile memory in chromium-doped SrTiO3 single crystals,xe2x80x9d Applied Physics Letters, Vol. 78, No. 23, 4 Jun. 2001, and xe2x80x9cElectric current distribution across a metal-insulator-metal structure during bistable switching,xe2x80x9d Journal of Applied Physics, Vol.90, No. 6, 15 Sep. 2001, all of which are hereby incorporated by reference for all purposes.
Similarly, magnetic RAM (MRAM) requires only two terminals to deliver a magnetic field to the memory element. Other two terminal devices include Ovonic Unified Memory (OUM), which uses chalcogenic layers of material, and various types of ferroelectric memory. With only two terminals, it has been theorized that memory can be arranged in a cross point architecture.
However, mere recognition that a two terminal memory element is theoretically capable of being placed in a cross point array does not solve many of the non-trivial problems associated with actually creating such a device.
The present invention provides a multi-output multiplexor. In one embodiment the multiplexor has a first port, a plurality of second ports, a plurality of control signals and a plurality of modulating circuits.
Each modulating circuit is in electrical contact with the shared first port, one of the second ports, and at least one of the control signals. If a control signal to a modulating circuit is in a first select mode, the modulating circuit passes substantially the entire voltage from the first port to its associated second port. If the modulating circuit""s control signal is in a second select mode, the modulating circuit only passes a portion of the voltage. Finally, if the modulating circuit""s control signal is in an unselect mode, the modulating circuit passes substantially no voltage from the first port to its associated second port.
In a preferred embodiment, the second port is in electrical contact with a gate circuit that is also in electrical contact with a reference voltage, such as ground. When the gate circuit is turned on, the second port associated with that modulating circuit goes to ground.